Post 48 –by Gautam Shah  (Lecture series: Space Perception -Article-III of 15)


The Illumination in a space is fairly consistent due the fairly steady source and predictability of the change. As one moves around a spatial field, things are perceived from different positions and in different contextual conditions. Other important factor that leads to changed perception is the increasing maturity of cognition. With the duration and proximity we learn lot more about the spatial field.

Light Corridor Hallway Shadows People Aisle View

There are many ways the eyes move. “Our eyes converge as well as diverge” according to the intensity of light and size of the field to be scanned. The fovea region in the retina of the eyes helps in perception movement. In even seemingly non-moving eyes, small jiggling movements, called micro-saccades to occur. The broadest movements occur with gestural movement of eyes and heads and shifting during postures.

Light And Shade Corridor Light Building

A spatial field has many depths.

Some fields, closer to the position of perception are illuminated with sources under our own control. Here the illumination conditions can be changed at will, or the position of perception shifted around. In both of these cases, the cause-effect has some certainty.

Bistro Dining Tables Restaurant Local Inn Table

Fields that are faraway from the position of perception are illuminated with sources under no-one’s control. Here the illumination conditions cannot be altered at will. Shifting the position of perception perhaps changes the contextual conditions, but the illumination component of the scene remains nearly static.


In very vast natural scapes the contrasts (changes) due to illumination are not highly noticed except in variable cloud cover, or during sunlight refraction at morning-evening periods.A brilliant sunrise, sunset or cloud formation in illuminated distant sky, show very little effect on the perception foreground of landscape’.


The effects of illumination are more pronounced and under control in restrictive space fields such as the built-forms, interior spaces and neighbourhood extents. Here the changes in contextual conditions accompany the changes in the foreground or components of the scene, so both seem controlled and restrained.



A spatial field is illuminated by natural light as Direct sun light, Sky Component (SC), Reflected Component (RC) of natural light, artificial illumination, and in many urban areas from surroundings’ lights like a street and vehicles. In addition to these sources, we use fluorescence to aid perception.

Fluorescence and phosphorescence are form of luminescence, or the emission of light by a substance that has absorbed light or other electromagnetic radiation.


The illuminants’ contexts are: strength and direction of source, background and foreground brightness, reflectance from surroundings, colour of light, multiplicity of sources. Other conditions include variability of space, objects and presence of dynamic (moving-vibrating) elements.

Built Space forms are occupied by objects, people and environmental effects but these rarely occur distinctly alone, in any rational form or within a nominal framing reference. The illuminants complicate the scene even if these elements manifest in for a fraction of a moment or remain unvaried for a very long period.


Single source illuminants are very definitive but complications arise due to the reflectance from many surfaces, directions, strength (brightness) and colour. Such complications are compounded with increasing number of original illuminants. Single illuminant defines a space and its objects in familiar sense, but fail as soon as the position of perception changes. Single illuminant is an irritant if any part of space has flickering movement (eg. Fan, moving curtains). Single illuminants are ideal for ‘object modelling’ as the shapes emerge without any compromises.


Perception ambiguities and compromises occur when an object or a group of overlapping objects, are lit by nearly same tonal colour value as the background. Indistinct figure-ground contrast, dissolve the edges. We tend to relate larger elements as the ground, over which smaller entities exist.

The objects are seen composition of surfaces that reflect incident light. Besides the variations caused by the angular exposition of surfaces, the surface quality or textures are detected by naked eye (at 0.07 mm). Smaller scale variations affect the gloss of the surface and mirroring effect of the surface. Very large surfaces have possibly no edges or breaks, and so are perceived through local variations of illumination.



Spatial forms are recognized with illumination references such as the proportionate extent of foreground-background, framing, strength of silhouettes, partial occlusion of elements, shading with the differing contrast and direction of the shadows, and diffusion by way of reflection, and refractions.

Stainless Design Stainless Steel Steel Building

Illuminated forms become difficult to recognize when an object curves around out of sight. Such occluding contours dissolve the edge of an object, and present poor silhouette formation. The absence of a well-defined contour renders the surface shapes (such as convex/concave) ambiguous.


The process of perception is a two-way affair. Position of a person and relative source of illumination are very important consideration for Space Planning. A person trying to project own-self must be aware of the perceiver’s distance, angles of connection, social dependency and postural condition. A strong back illumination, makes it difficult to perceive a chair-person’s features and gestures.

Concert Instrument Bass Sound Music Guitar Rock

Position of a person relative to the source of illumination also holds true in conference rooms, executive cabins, reception areas, lecture rooms, press conference rooms, etc. Natural or artificial illumination -as singular source and that too from the backside must be avoided, and if inevitable, reinforce it with lighting from other directions. One of the simplest ways is to envision how the situation manifests from every single position.

The daytime happenings, change considerably at supper time, as the ‘backbite window’ illumination is replaced with artificial lighting. Nominally the situation should stand corrected (if not reversed), but attitudes formed during daytime persist at other times. Shops in business districts are low illuminated because the staff is occupying the space for longer time and so is accustomed to low level (or even to save power), but customer entering from bright outside finds the darkness discouraging.

Side illumination eliminates many of the anomalies of perception and recognition but not all. To create good diffusion, the source for side illumination needs some depth from the occupying position. In small rooms this is rather difficult and requires careful design.


We are more used to illumination from top. But very strong such sources create under the chin shadows. This can be corrected by illumination from other directions, or from floor and table top reflections. Light colour floors and table tops, needs to be excluded from TV camera shooting angles. This is done by positioning the participants on a raised platform, and cameras at a slightly lower level then the table tops.


This is the III article (of intended 15) in series ‘Space Perception‘ that will form a course of One semester.



SOME SOUND BITES -Space Perception -I

Post –46  by Gautam Shah (Lecture series: Space Perception -Article-I of 15)



Sound is caused by disturbance or vibration in an elastic material. That energy of vibration is perceived as a subjective experience by the human ear. Ears capture, transmit and transduce the sounds by discriminating the sounds of different frequencies, and perceiving the same in different manners.


Human ear can perceive sound above infra-sound 20 Hz, and below ultrasound 20000 Hz, but more importantly human ears can discern information from sound and noise. Range of Human voice is from 60 Hz to 10000 Hz, but 90 % intelligibility occurs 200 Hz to 4000 Hz.

NASA Orion acoustics test

A modern good quality PA system should be capable of 100 Hz to 6000 Hz and preferably 10000 Hz. For music the PA system should be 80 Hz to 10000 Hz and up to 15000 Hz for high quality theatre type of installation. Telephone voices have peculiar ‘unnatural’ feel because voice frequencies below 400 hertz and above 3,400 hertz are eliminated.


When machines are taught to speak like humans, the process of learning (AI) is to break human speech into phonemes (each of 30 micro seconds slots). This forms the basic set and used for enunciation, so when robots speak, they sound monotonic, stilted and mechanical.

Human speech consists of two parts: vowels and consonants. In general vowels are easily recognized because they are distinctive and especially the `deeper’ or the longer vowels occupy more time than any other speech component. They also consist mostly of lower speech frequencies. The formative characteristics of the mouth, based on the cavity resonance, are responsible for vowel sounds, and the main vehicle for the intelligibility of the speech.

Arnold_Lakhovsky_ConversationConsonants are less easy because they occupy a very short time and so seem transient. These mostly are of higher speech frequencies (1200 Hz). There are many more of them than vowels and so offer speech audibility and perception. Consonants provide the rich sound variants that make different speeches different.

BushIn addition to the formats, sibilants, it is a consonant, with characteristic hissing sound (such as sh, s, z, and zh), and stops of various types (consonant sounds such as b, p, d, t, g, k) are characterized by the momentary blocking of some part of the oral cavity, help in high intelligibility.


The sound perception and cognition system has the ability of compensating and filling in the required information in terms of vowels, consonants, and even words into speech or sentences. The time required to fill in the required information is provided by the quality of acoustics of the space.A longer reverberation seems to elongate the spoken sound in time scale, but an excess of reverberation may mask the following sounds. A fast orator in a reverberating hall fails to impress the audience, whereas a slow speaker in well absorbent and non reverberating space may seem discontinuous.’

Rousselots_Apparat_zur_Aufzeichnung_der_SpracheSpeech intelligibility depends on the quality of space. The space, size, shape, materials and the PA system (if any) define how the speech will be perceived. Seasoned speakers or stage performers (actors, singers) have innate sense on how to improvise the tonal quality of delivery. They overcome (masking) the effect of background noise by raise the voice and change the range of frequency. In spaces with longer reverberation the pauses are widened. Speakers face the section of crowd they want to address, to direct the original sound and allow them (section of crowd) to read the lips and body gestures.


Speakers (orators, actors and singers) and Listeners, all hear original sound as well as reflected sounds, but in completely different spatial context (space, size, shape, materials and the PA system). For listeners the most important matter is the identification (real or mythical) of the source of sound, in spite of the ‘presence of many reflected sounds’. This helps in personalization or being part of the event. However if the time gap between the hearing of original sound and reflected sound is more than two seconds, the localization begins to be difficult. In long or a deep hall the P.A. system sounds arrives stronger and even before the arrival of direct sound creating confusion including visual and aural synchronization of lip and other body posture-gesture language with the spoken sound.


In case of speech, a short sound reverberation time, implies high absorption, which makes, in the rear seats, a speech registration difficult. On the other hand, a long reverberation time means, the sound of each syllable is heard against the reverberant sound of previous syllables.


This is the I st article of the series on SPACE PERCEPTION